Molality
Definition and meaning of Molality in chemistry.
Molality is a measure of the concentration of a solute in a solution, expressed as the number of moles of solute dissolved per kilogram of solvent.
In more detail
Unlike molarity, molality is temperature-independent because it uses mass rather than volume, making it particularly useful in studying colligative properties such as boiling point elevation and freezing point depression. The symbol for molality is m, and its unit is mol/kg. Because molality depends only on the ratio of solute particles to solvent mass, it remains constant regardless of temperature changes.
Key facts
| Symbol | m |
|---|---|
| Unit | mol/kg |
| Definition | Moles of solute per kilogram of solvent |
| Temperature-dependent | No |
| Field | Physical Chemistry |
A solution prepared by dissolving 1.0 mole of sodium chloride (NaCl) in 1.0 kilogram of water has a molality of 1.0 m.
Frequently asked questions
How is molality different from molarity?
Molality uses mass of solvent (kilograms) while molarity uses volume of solution (liters). Because molality is independent of temperature, it accurately predicts colligative properties like boiling point elevation and freezing point depression.
Why use molality instead of molarity?
Molality is preferred for studying temperature-dependent phenomena because its value does not change with temperature changes, whereas molarity changes as solution volume expands or contracts.